Adducts



United States Patent 3,347,893 ADDUCTS John N. Hogsett, Charleston, Albert Khuri, South Charleston, and Helmut W. Schulz, Charleston, W. Va., assignors to Union Carbide Corporation, a corporation of New York No Drawing. Filed Dec. 27, 1961, Ser. No. 162,183

' 20 Claims. (Cl. 260-448) This invention relates to the preparation of adducts of metal borohydride with a ligand composed solely of carbon, hydrogen, boron, and amino nitrogen atoms. In various aspects, the invention relates to liquid propellant and solid propellant systems which utilize said novel adducts as a fuel component therein.

In recent years, industry has been actively engaged in the search for fuels which are suitable for propellant systems. While various fuel compositions have been suggested and tried for such purposes, limited success has been achieved in view of the exacting requirements of the art. Among the more important characteristics of, for example, a liquid fuel can be listed (1) high specific impulse, (2) relatively high density, (3) liquid state over a wide temperature range, (4) low freezing point, (5) hypergolicity with common oxidizers, and (6) ease of handling without undue hazard. Since the above enumerated characteristics are not all consistent with one another, a balance or compromise must be made.

Metal borohydrides, such as aluminum borohydride, beryllium borohydride, and zirconium borohydride, because of their potentially high heat release, have aroused some interest in the past as a fuel in rocket systems. However, the violent chemical reactivity and thermal instability of, for example, aluminum borohydride and beryllium borohydride, have created handling and storage problems which have precluded their serious consideration as storable rocket fuels. For instance, aluminum borohydride and beryllium borohydride inflame violently in air and react vigorously with water. Moreover, beryllium borohydride suffers from the disadvantage of being extremely toxic. The density of aluminum borohydride being 0.55 gram/milliliter, at 25 C., further detracts from its desirability as a rocket fuel since large tankage would be required to sustain long range rocket flights. The disadvantages which result from increased missile weight due to large fuel storage tanks are obvious. In addition, though aluminum borohydride and beryllium borohydride are generally not regarded as shock-sensitive, there is little experimental evidence on this point since these materials are so difiicult to handle in the test apparatus normally employed for such determinations.

In accordance with the instant invention, it has been discovered that the reaction of a metal borohydride, i.e., aluminum borohydride, beryllium borohydride, or zirconium borohydride, with a ligand composed solely of carbon, hydrogen, boron, and amino nitrogen atoms, results in novel adducts which have exceptional and valuable utility in various fields of application. These novel adducts, as the fuel component in a propellant system, possess a combination of well balanced properties, especially the novel liquid adducts when employed as hypergolic fuels. The novel solid adducts can be used as energetic additives in solid propellants. The novel adducts, also, are useful as additives in fuels for conventional airbreathing engines whereby the combustion and flame-out characteristics of the hydrocarbon jet fuels are improved. The novel adducts have further utility as additives to liquid hydrocarbon rocket fuels in bipropellant rocket engines employing oxidizers such as liquid oxygen or nitrogen tetroxide wherein the presence of said novel adducts improves the combustion characteristics of said 3,347,893 Patented Oct. 17, 1967 propellant systems as, for example, by preventing combustron instability or resonant burning.

In addition, the physical properties of the novel ad- I ducts are dramatically more desirable than the corresponding metal borohydride per se. For example, the novel adducts are more stable, and less hazardous than the parent metal borohydride. In general, the densities of the aluminum borohydride adducts are markedly higher than the density of aluminum borohydride.

Accordingly, one or more objects will be achieved by the practice of the invention.

It is an object of the invention to provide novel adducts of various metal borohydrides with ligands composed solely of carbon, hydrogen, boron, and amino nitrogen atoms. Another object of the invention is directed to providing novel processes for preparing the aforementioned adducts. A further object of the invention is directed to the preparation of novel high energy fuels of well balanced properties for use in propellant systems. A still further object of the invention is directed to novel adducts which are useful as additives in conventional fuels, e.g., jet fuels for air-breathing engines, and hydrocarbon fuels for use in liquid bipropellant rocket motors, to thus improve the combustion characteristics and the hypergolicity of said fuels. Another object of the invention is to provide novel adducts which are useful as fuels for the generation of a driving fluid for power turbines such as auxiliary power turbines in spacecraft or underwater propulsion systems utilizing, for example, sea water as an oxidizer component. Other objects of the invention are directed to the preparation of novel adducts having utility as reducing agents, stabilizers, color improvers, etc., which are useful in various fields of application such as in the refining of organic liquids, synthetic resins, and the like. These and other objects will become apparent to those skilled in the art from a consideration of the instant specification.

The broad aspect of the invention encompases novel adducts of aluminum borohydride, beryllium borohydride, or zirconium borohydride with a ligand composed solely of carbon, hydrogen, boron, and amino nitrogen atoms.

The ligands which are contemplated as a reagent in the preparation of the novel adducts are further characterized in that they contain at least one amino nitrogen atom which functions as a Lewis base. In accordance with the Werner coordination theory, the resulting novel adducts, from a structural interpretation, can be characterized as containing at least one amino nitrogen to metal coordinate bond. It should be noted that of all the amino nitro gen atoms of the ligand which can function as a Lewis base, at least one of said amino nitrogen atoms is coordinately bonded to a metal atom (of the metal borohydride). In addition, the metal atom (of the metal borohydride) can be coordinately bonded to more than one amino nitrogen atom which functions as a Lewis base. However, as indicated previously, the ligand must contain at least one amino nitrogen atom which functions as a Lewis base. It is preferred that the ligand contain up to 4 amino nitrogen atoms in the molecule. It is preferred, also, that any hydrocarbon substituents which are monovalently bonded to the amino nitrogen atoms be alkyl groups which contain up to 12 carbon atoms, and preferably still, up to 3 carbon atoms. Methyl substituents on the amino nitrogen atoms are highly preferred. It is further pointed out that the word adduct(s), as used herein including the appended claims is employed in its broadest sense and encompasses within its scope complexes, coordination compounds, chelates, and the like.

In one aspect, the invention encompasses novel adducts of metal borohydrides with ligand composed solely of carbon, hydrogen, boron, and amino nitrogen atoms in which at least one amino nitrogen atom functions as a Lewis base. In another aspect, the ligand is composed solely of carbon, hydrogen, boron, and amino nitrogen atoms in which each amino nitrogen atom is monovalently bonded to a boron atom. In still another aspect, the ligand is composed solely of carbon, hydrogen, boron, and amino nitrogen atoms in which each amino nitrogen atom is monovalently bonded to a boron atom, in which at least one amino nitrogen atom functions as a Lewis base, and in which the amino nitrogen atoms are present in the form of secondary amino groups and/or tertiary amino groups.

In a particularly preferred aspect, the novel adducts of the invention can be represented by the following formula:

where L is a ligand composed solely of carbon, hydrogen, boron, and amino nitrogen atoms, wherein each amino nitrogen atom is monovalently bonded to a boron atom; wherein at least one amino nitrogen atom functions as a Lewis base; wherein M represents aluminum, beryllium, or zirconium; wherein x is the valence of M; and wherein n is an integer having a minimum value of one and a minimum value no greater than the total number of amino nitrogen atoms contained in the ligand (L) which function as Lewis bases. Consequently, the maximum value of n will be determined by the number of amino nitrogen to metal coordinate bonds present in the novel adduct. This in turn will be governed by the choice of the ligand and, in general, by the proportions of the reagents, i.e., ligand and metal borohydride, which are employed in the preparation of the novel adducts. For example, the ligand tetra(dimethylamino)diboron has four amino nitrogen atoms which theoretically can function as Lewis bases. Equimolar ratios of aluminum borohydride and this compound will react to yield a white solid adduct. On the other hand, a ratio of two moles, or more, of aluminum borohydride per mole of this ligand also yields a white liquid adduct. Any aluminum borohydride in excess of the 2 to 1 molar ratio can be recovered as unreacted reagent. Thus, in the light of the preceeding illustrations (as well as the operative examples in the specification), it is readily apparent that the number of amino nitrogen atoms which are capable of functioning as Lewis bases realistically governs the maximum value of the variable 11 in Formula I supra. It is preferred that n be an integer having a value greater than zero and less than 5, and preferably still, greater than zero and less than 6.

Illustrative ligands which are contemplated in the preparation of the novel adducts include, among others, the tetra (hydrocarbylamino)diborons, e.g., tetra(alkylamino)diboron, tetra(cycloalkylamino)diboron, tetra(arylamino) diboron, tetra(aralkylamino)diboron, tetra(alkarylamino) diboron, and the like; the tetra(dihydrocarbylamino)diborons, e.g., tetra(dialkylamino)diboron, tetra(clicyclo alkyl)diboron, tetra(diarylamino) diboron, tetra(dialkarylamino)diboron, tetra(diaralkylamino)diboron, and the like; the tris(dihydrocarbylamino)boranes, e.g., tris(dialkylamino)borane, tris(diarylamino)borane, and the like; the tris (hydrocarbylamino)boranes, e.g., tris(alkylamino) borane, tris(arylamino)borane, tris(alkarylamino) borane, and the like. Specific ligands include, for example, tetra(methylamino)diboron, tetra(ethylamino)diboron, tetra(isopropylamino)diboron, tetra(nhexylamino)diboron, tetra(n-octylamino)diboron, tetra(n-dodecylamino) diboron, tetra(cyclohexylamino)diboron, tetra(anilino)diboron, tetra(p-toluidino) diboron, tetra(dimethylamino) di boron, tetra(diethylamino)diboron, tetra(di-n-pentylamino)diboron, tetra(di-n-hexylarnino)diboron, tetra(din-dodecylamino diboron, tetra(dicyclohexylamino) diboron, tetra(diphenylamino)diboron, tris(dimethylamino) borane, tris(dietbylamino)borane, tris(din-propylamino) borane, tris(di-n-hexylamino)borane, tris(di-n-decylamino) borane, tris (diphenylamino)borane, tris(dicycl0- hexylamino borane, tris (methylamino) borane, tris (ethylamino) borane, tris (n-propylamino) borane, tris (n-hexylamino) borane, tris (toluidino borane, tris anilino borane, and the like.

Preferred ligands include the tetra(alkylamino)diborons, the tetra(dialkylarnino)diborons, the tetra(alkylamino)boranes, and the tris(dialkylamino)boranes. Especially preferred ligands are the tetra[(l0wer alkyl) amino]diborons, the tetra[di(lower alkyl)amino]diborons, the tris[(lower alkyl)amino]boranes, and the tris[di(lower alkyl) amino1boranes.

It is pointed out that by the term hydrocarbyl, as used herein including the appended claims, is meant the monovalent organic radical which is composed of carbon and hydrogen and which is free of ethylenic and acetylenic unsaturation. Illustrative hydrocarbyl radicals include alkyl, cycloalkyl, aryl, aralkyl and alkaryl. The limitation lower before the work alkyl, as used herein including the appended claims, restricts said alkyl to those containing 1 to 6 carbon atoms. The tetraamino substituted diborons have the skeletal structural formula whereas the tris-amino substituted boranes have the skeletal structural formula Illustrative novel adducts which are encompassed within the scope of the invention include, among others, the adducts of aluminum borohydride with tetra(methylamino)diboron, aluminum borohydride with tetra(ethylamino)diboron, aluminum borohydride with tetra(n-hexylamino)diboron, aluminum borohydride with tetra(n-decylamino)diboron, aluminum borohydride with tetra(anilino) diboron, aluminum borohydride with tetra(dimethylamino)diboron, aluminum borohydride with tetra(diethylamino)diboron, aluminum borohydride with tetra(di-nhexylamino)dibor0n, aluminum borohydride with tetra(diphenylamino)diboron, aluminum borohydride with tris(dimethylamino)borane, aluminum borohydride with tris(diethylamino)borane, aluminum borohydride with tris-(di-npropylamino)borane, aluminum borohydride with tris(din-hexylamino)borane, aluminum borohydride with tris (methylamino)borane, aluminum borohydride with tris (ethylamino)borane, aluminum borohydride with tris(nhexylamino)borane, aluminum borohydride with tris(anilino)borane, aluminum borohydride with tris(toluidino)- borane, aluminum borohydride with tris(cyclohexylamino)borane, aluminum borohydride with tris(benzylamino)borane, and the like. Other illustrative novel compositions include the beryllium borohydride and the zirconium borohydride adducts of the above.

The novel adducts can be prepared by contacting the metal borohydride with the ligand under an inert, anhydrous atmosphere, e.g., hydrogen, nitrogen, argon, helium, krypton, and the like. If desired, an inert normally-liquid, organic vehicle, described hereinafter, can be employed. It is essential that impurities such as oxygen, carbon dioxide, carbon monoxide, water, and other materials which are reactive with metal borohydride be avoided in the system in view of the highly hazardous and explosive nature of the borohydride reagent. The operative temperature can be in the range of from about 64 C., and lower, to below the boiling point of alumnium borohydride, e.g., from about 64 C. to 43 C. A preferred temperature range is from about 0 C. to about 30 C., and preferably still, from about 15 C. to about 25 C. The order of addition of the reagents does not appear to be narrowly critical.

However, it is preferred that the metal borohydride, preferably contained in an inert normally-liquid organic vehicle, be added to the ligand. Incremental isothermal addition of the metal borohydride to be ligand, with slow stirring, is highly preferred. If desired, the reaction mixture can be cooled to maintain the desired reaction temperature. The operative pressure can be subatmospheric, atmospheric, or moderately superatmospheric. In general, suitable results have been obtained by conducting the reaction below about 760 mm. of Hg pressure. It is preferred that the operative pressure be in the range of from about mm. of Hg to about 760 mm. of Hg. For relatively large batch production of the novel adducts, it was observed that satisfactory results were obtained by effecting the reaction under essentially atmospheric pressure.

In view of the hazardous nature of the metal borohydride, it is not preferred to have a large excess of unreacted metal borohydride present in the reaction product mixture. In the preparation of the novel liquid adducts, the preferred maximum concentration of metal borohydride is in slight excess of the quantity which is necessary to react with the ligand to produce the desired liquid adduct. On the other hand, when employing relatively high boiling ligands ,to prepare the novel liquid adducts, the presence of unreacted ligand in the resulting reaction product mixture is undesirable since the resolution of said mixture, by distillation, could result in the thermal decomposition of the liquid adduct product. However, this disadvantage does not present itself when the resulting product is a solid adduct. In such cases, the solid adduct, if insoluble in the re action product mixture, is readily recovered therefrom via filtration techniques. Should the solid adduct be soluble in the reaction product mixture, the addition of an inert, normally-liquid, organic vehicle thereto in which the solid adduct product is insoluble and the relatively high boiling ligand is miscible, would result in the precipitation of said solid adduct. The solid adduct then could be recovered by filtration procedures, as indicated previously. Subject to the variables illustrated above, it is desirable to employ an amount of metal borohydride which is slightly in excess of that required to react with the total amount of ligand to produce the desired novel liquid adduct, whereas it is desirable to employ an amount of ligand which is moderately in excess of that required to react with the total amount of metal borohydride to produce the desired novel solid adducts. However, it is preferred to employ essentially stoichiometric amounts of the reagents.

The reaction period will depend, to a significant extent, upon various factors such as the choice of the ligand and metal borohydride, the concentration of the reactants, the operative temperature, the operative pressure, the manner of addition of the reactants, the use of an inert, normallyliquid, organic vehicle, and other considerations. Depending upon the correlation of the variables illustrated supra, the reaction period can range from several minutes to a few days. However, highly satisfactory results have been obtained by conducting the reaction over a period of from 0.5 hour, and lower, to about 6 hours, and higher.

If desired, the reaction can be effected in the presence of an inert normally-liquid, organic vehicle, i.e., a vehicle which is non-reactive with the reagents or the resulting novel adduct product. Illustrative vehicles include, for eX- ample, the normally-liquid saturated aliphatic and cycloaliphatic hydrocarbons, e.g., n-pentane, n-hexane, n-heptane, iso-octane, n-octane, cyclopentane, cyclohexane, cycloheptane, methylcyclohexane, ethylcyclopentane, and the like; the aromatic hydrocarbons, e.g., benzene, toluene, xylene, ethylbenzene, and the like; and other inert, normally-liquid, organic vehicles which would become readily apparent to one skilled in the art. The use of an inert vehicle permits the heat of reaction to be more evenly dispersed, thus minimizing the danger of inadvertently causing thermal decomposition of unreacted metal borohydride. This advantage is especially desirable when employing large quantities of reagents.

The novel adduct product can be recovered from the reaction product mixture by various procedures known to the art. For example, excess reagent and inert vehicle, if any, can be recovered from the reaction product mixture by distillation under reduced pressure, e.g., 10 to 50 mm. of Hg. The novel solid adducts also can be recovered from the reaction product mixture by filtration or crystallization techniques. Vacuum distillation is a preferred method of recovering the novel adduct product providing it can be vacuum distilled without decomposition.

The preparation of aluminum borohydride, beryllium borohydride, and zirconium borohydride 3 is documented in the literature.

The tris-amino substituted boranes can be prepared by the slow addition of a solution of boron trichloride in an inert, normally liquid organic vehicle, e.g., pentane, to a solution containing a stoichiometric excess of a primary amino (RNH or a secondary amine (R NH) in an inert, normally liquid organic vehicle, e.g., pentane, under stirring, and cooling via an ice water bath. Thereafter, the resulting solid amine hydrochloride is filtered from the reaction product mixture, followed by removing the pentane from the filtrate via distillation under reduced pressure. The residue then is subjected to redistillation under reduced pressure. There is obtained a product having the following formulas:

wherein the R radical can be alkyl, e.g., methyl, ethyl, n-propyl, etc.; aryl, phenyl, tolyl, xylyl, etc.; aralkyl, e.g., phenethyl, etc.; cycloalkyl, e.g., cyclohexyl, etc.; and the like. The use of a primary amine (RNH reagent in the above reaction gives tris(hydrocarbylamino)borane whereas the use of a secondary amine (R NH) reagent results in tri[di(hydrocarbyl)-amino]borane.

The tetra-amino substituted diborons can be conveniently prepared in the following manner. A solution of boron tribromide in pentane is slowly added to, for example, tris(dialkylamino)-borane such as tris(dimethylamino)borane, in an inert, normally liquid organic vehicle, e.g., pentane, under vigorous stirring, at a temperature of about -50 C. Thereafter, the pentane is rapidly distilled therefrom at 1.5 mm. of Hg. Distillation of the resulting residue gives bromo-bis(dialkylamino)borane. The bromo-bis(dialkylamino)borane then is dissolved in an inert, normally liquid organic vehicle, e.g., toluene, and the resulting solution is slowly added to highly dispersed molten sodium in toluene at about C. After about 4 hours, the solids resulting therefrom are filtered, followed by removing, under vacuum distillation, the toluene from the filtrate. After subjecting the residue to distillation, there is obtained tetra(dialkylamino)diboron as the resulting product. Transamination of, for example, tetra- (dimethylamino)diboron, with an excess of a primary amine (RNH or a secondary amine (R NH) gives:

1 U.S. Patent No. 2,599,203. 2 Burg et al., J. Am. Chem. 800., 62, 3425 (1950). 8 U.S. Patent No. 2,575,760.

respectively, wherein the R radical can be alkyl, e.g., methyl, n-hexyl, etc.; aryl, e.g., phenyl, etc., cycloalkyl, e.g., cyclohexyl, etc.; and the like. The transamination reaction is conveniently carried out in a sealed bomb at moderately elevated temperatures, e.g., 75 C. for a period of several days, e.g., 100 hours, or more. The excess primary amine or secondary amine is recovered from the resulting reaction product mixture via distillation techniques under reduced pressure. Distillation of the residue under high vacuum, e.g., 0.5 mm. of Hg at 25 C., gives a high purity transamination product.

A preferred embodiment of the invention is directed to the preparation of novel liquid propellant systems which utilize the novel liquid adduct as the fuel component. Many of the novel liquid adducts are highly attractive in that they are capable of giving a high specific impulse with appropriate oxidizers when used as liquid fuels in liquid propellant systems. As is well known, the specific impulse is a measure of the pounds of thrust obtainable per pound of propellant (fuel+oxidizer) reacted per second. A higher specific impulse makes possible an increased range or trajectory of a vehicle driven by jet propulsion, or an increased payload, or a decreased fuel requirement, or a higher velocity at burnout.

Examples of appropriate liquid oxidizers, both storable and cryogenic include nitrogen tetroxide, the fuming nitric acids, chlorine trifluoride, hydrogen peroxide, bromine pentafluoride, oxygen, fluorine, oxygen difluoride, perchloryl fluoride, perfiuoroguanidine, and others. The ratio of oxidizer to novel fuel is generally chosen so as to maximize the specific impulse delivered by the given propellant system, except when said propellant system is employed in a gas generator to furnish hot compressed, driving fluid to power a turbine. When used for gas generation, it is generally advantageous to employ a fuelrich ratio so as to limit the temperature of the combustion products in order to avoid heat damage to the turbine. Another important advantage of various novel liquid adducts is their ability to form hypergolic propellant systems with certain liquid oxidizers that normally do not effect hypergolic combustion with common rocket fuels. Hypergolic combustion is particularly important in spacecraft propulsion which may require intermittent combustion and variable thrust capabilities.

Another preferred embodiment of the invention is directed to the preparation of novel solid propellant formulations which utilize the novel solid adducts as a fuel component. Solid rocket propellants can be termed monopropellants in that a solid oxidizer and solid fuel are mixed together in a single matrix which does not require the addition of oxidizer from an external source. An important class of solid propellant systems are known as composite solid propellants which can be prepared by suspending a solid oxidizing agent in a liquid prepolymer which is capable of being cast and cured to a combustible elastomeric matrix. Composite solid propellants can be made in a great variety of compositons. Various constituents can be added to modify the characteristics of the propellant such as to improve the energetics, to improve the physical properties, to catalyze or retard the burning process, and the like. Oxidizers which can be employed include, for example, ammonium perchlorate, ammonium nitrate, nitronium perchlorate, hydrazine nitrate, hydrazine perchlorate, quanidinium perchlorate, and others. Exemplary binders include polyethylene, the butadieneacrylic acid copolymers, the polyether polyurethanes, the fluorocarbons, and other elastomeric binders. A typical standard solid propellant composition can contain about 65 weight percent ammonium perchlorate, 15 weight percent polymeric hydrocarbon binder, and 20 weight percent aluminum powder which would produce upon combustion (at 1,000 p.s.i.) a theoretical specific impulse of about 265 pounds-second/pound. However, the actual delivered specific impulse has been somewhat less. To improve the performance of such solid propellant systems,

the subject embodiment contemplates the use of the novel solid adducts as a high energy solid fuel additive to replace part or all of the less energetic fuel additives, such as aluminum, now commonly used. As is readily apparent to those skilled in the art, the quantity and choice of the novel solid adduct to be incorporated to form the novel solid propellant in order to achieve well balanced properties and optimum performance will be governed by various factors such as the compatibility with the chosen binder, the thermal stability of the novel adduct, the oxidizer of choice, the nature and concentration of burning rate modifiers, and other considerations. In a preferred aspect, the novel solid adduct is encapsulated within a combustible material such as, for example, polyethylene, polypropylene, aluminum, polytetrafiuoroethylene, polyalkyl siloxanes, and the like. The art is well-apprised of the technique of encapsulating a solid fuel component which is to be incorporated in a solid propellant.

Another preferred embodiment of the invention relates to novel compositions of liquid fuels which contain the novel adduct in an amount sufiicient to improve the combustion characteristics, ignition efficiency, flame stability, and/or energetics of said liquid fuel. The liquid fuels which are contemplated are useful as fuels for jet propulsion purposes which include, among others, air-breathing engines and liquid rocket engines, e.g., turbojets, ramjets, bipropellant rockets, and other combustion power plants. Although a maximum increase in specific impulse is produced by using a maximum quantity of the novel adduct, other practical considerations connected with the particular applications of the fuel often lead to preferred mixtures containing less than the maximum compatible quantity of novel adduct. The attainment of well balanced properties in the novel liquid fuels is governed by many of the variables discussed previously, e.g., choice of liquid fuel, the choice of the novel adduct solubility, specific application of the novel liquid fuel, the addition of modifying components, hypergolicity, and economic factors. Illustrative liquid fuels include the aliphatic, hydroaromatie, and aromatic hydrocarbons, and mixtures thereof, for example, kerosene (RP-1, JP-4, JP-5, JP-6), n-hexane, diethylcyclohexane, petroleum ether (boiling range 3060 (3.), benzene, toluene, xylene, and the like; aliphatic, aromatic, and heterocyclic amines such as isopropylamine, diethylamine, aniline, cyclohexylamine, pyridine, and the like; cyclic ethers such as dioxane, furan, tetrahydrofuran; and others.

Additional embodiments which are contemplated within the scope of the invention involve the use of the novel adducts as color improvers, as stabilizers, as reducing agents, as antioxidants, as redox catalysts, as catalysts for olefin polymerization processes, and so forth. Contaminants such as carbonyl compounds in oxygenated organic compounds, e.g., Oxo alcohols, are readily reduced by incorporating a small quantity of the novel adduct thereto. Of course, contaminated oxygenated organic compounds such as aldehydic compounds that can react with the novel adduct are not applicable. The amount of novel adduct which can be added, in general, is approximately sufficient to react with the contained contaminants. Oxidative degradation which results from traces of oxygen or oxygen-containing compounds contained in, for example, synthetic polymers, can be prevented by incorporating into said polymers an antioxidant amount of the novel adduct. The novel adducts can be employed as catalysts for the polymerization of olefins, ethylene, propylene, the butylenes, styrene, etc., preferably via the so-called low pressure techniques. The optimum catalyst concentration is readily apparent to those skilled in the art.

As is well known, the heat of formation of a compound can be defined as the enthalpy change upon forming said compound from its elements in their standard state. The heats of formation of the ligands and the metal borohydrides were calculated from standard heats of combusimpulse data presented herein were determined by making performance calculations at selected oxidant to fuel ratios, and then plotting the results to define the maximum specific impulse and the optimum oxidant to fuel ratio. In general, the calculations were performed on an IBM 7090 computer using a chemical equilibrium program prepared by the US. Naval Ordnance Test Station together with thermodynamic data for combustion species supplied with the program. In a few instances, the performance curves were extrapolated to low oxidant to fuel ratios by computing additional relative specific impulse values by the approximate NARTS hand calculation method, with thermodynamic data for combustion products supplied with the method.

By the term energetics, as used herein, is meant the chemical energy release upon combustion, or, more particularly, the theoretical specific impulse.

The following examples are illustrative.

Example 1 A. Iso-octane was arbitrarily chosen as a solvent for studying the reaction of aluminum borohydride with tetra(dimethylamino)diboron (4DD). Use of a liquid medium enables a more rapid and safer addition of aluminum borohydride by acting as a heat sink and a dispersing agent for the reactants.

Dry iso-octane, 5 ml., 3.45 g., was charged into a 25 ml. flask equipped with a standard taper joint and a Teflon coated magnetic stirring bar. The flask was then attached to the high vacuum system, cooled with a liquid nitrogen bath, and evacuated to at least mm. of mercury. Aluminum borohydride, 2.28 mmoles, was measured in a-standard bulb and then added to the iso-octane which was frozen with liquid nitrogen. The resulting mixture was allowed to warm to room temperature and stirred until the pressure remained constant. The pressure was 94.2 mm. of Hg at 260 C. Another addition of aluminum borohydride, 1.96 mmoles, was made malc'ng the total 4.24 mmoles, and the above procedure repeated. The pressure was 122 mm. of Hg at 26.0 C.

Tetra(dimethylamino) diboron, 0.472 g., 2.39 mmoles,

' and 5 ml. of dry iso-octane were placed in a 25 ml. re-

action flask with a stirring bar just as above, attached tothe vacuum line, and pumped down to at least 10* mm. of mercury. The mixture was then allowed to Warm to room temperature and equilibrate. The pressure was 61.0 mm. of Hg at 260 C. Aluminum borohydride, 8.98 mmoles, was measured in the standard bulb and subsequently added, in increments, to the diboron-iso-octane admixture which was maintained at liquid nitrogen temperature. After each addition, the liquid nitrogen bath was removed and the reaction flask allowed to warm to room temperature, i.e., about 26 C., stirring initiated, and the pressure of the system recorded after equilibration. Observations made during the experiment were also recorded. The results are summarized in Table I.

G. R. Hendrick, Ind. and Eng. Chem., 48,1No. 8, p. 1366, August 1956.

r 5 The Theoretical Computation of Equilibrium Compositions, Thermodynamic Properties and Performance Characteristics of Propellant Systems, -NAVWEPS Report 7043, June 8, 1960.

a .T. D. Clark, The NQD Method of 1517 Calculation, Letter Report L-23, Naval Air Rocket Test Station, Lake Denmark, N.J., September 1959.

TABLE L-PRESSURE-COMPOSITION DATA FOR THE REACTION or ALUMINUMBOROHYDRIDE WITH TETRA (DIMETHYLAMINO)DIBORON IN ISO-OCTANE AT 26 0.

1 Tetra(dimethylamino)diboron.

The results indicate that the pressure was constant until a mole ratio of Al(BH /4DD was two. At higher mole ratios, the pressure increases corresponded closely to mixtures of unreacted aluminum borohydride and isooctane. The amount of unreacted aluminum borohydride, as determined by the pressure, was about 4.2 mmoles. Therefore, about 4.8 mmoles of aluminum borohydride reacted with 2.39 mmoles of 4DD, a mole ratio of about two.

The excess aluminum borohydride and iso-octane weredistilled from the reaction flask. The residue, i.e., tetra- (dimethylamino)diboron dialuminum borohydride, was a slightly yellow liquid with a vapor pressure of about 2.0 mm. of Hg at 26.0 C. This adduct was soluble in both iso-octane and kerosene. The tetra(dimethylamino) diboron monoaluminum borohydride was a white solid. Other physical properties of the liquid tetra(dimethylamino)diboron dialuminum borohydride compound include a density of approximately 0.900 gm./ml. at 20 C a freezing point greater than 40 C. stability of C.

B. In an analogous manner as part A above, when tetra(anilino)diboron is employed in lieu of tetra(dimethylamino)diboron, there is obtained an aluminum borohydride adduct of tetra(anilino)diboron.

C. In an analogous manner as part A above, when beryllium borohydride and tris(dimethylamino)borane are and a thermal employed in lieu of aluminum borohydride and tetra A. Tetra(methylamino)diboron, 0.555 gram, 3.92 mmoles, was transferred by means of a hypodermic needle into a 25 ml. flask which contained a Teflon coated magnetic stirring bar. The flask was attached to a high vacuum system, cooled with liquid nitrogen, and evacuated to at least 10* mm. of mercury. Aluminum borohydride, measured as a gas, was added incrementally to the diboron compound which was frozen with liquid nitrogen. The mixture was then allowed to slowly warm to room temperature, i.e., about 26 C., by removing the liquid nitrogen bath. After a period of about fifteen minutes, the flask was cooled with liquid nitrogen and the non-condensable gases measured in a Toepler pump. The reaction flask was then allowed to warm to room temperature and the equilibrium pressure recorded. When the mole ratio of aluminum borohydride to tetra(methylamino)diboron was one, the product was a white solid and subsequent reaction with gaseous aluminum borohydride was extremely slow. Benzene was then added to dissolve the solid product. The reaction of more aluminum borohydride proceeded readily because no pressure TABLE II.PRESSURE-COMPOSITION DATA FOR THE REACTION OF ALUMINUM BO ROHYD RIDE WITH 'lETRA (METHYLAMINO) DIBORON AT 26 C.

Al(BH4)a Total Hz added, Mole ratio, presevolved, curnula- Al(BH4)3/ sure, cumula- Remarks tive diboron mm. of tive mmoles Hg mmoles 0.775 0.183 28.0 0.538 White solids forming. 1. 85 0. 473 40. 5 1. 20 Contents of flask, all

white solids. 4. 02 1.03 22. 1. 61 Product mostly solid.

Some liquid detecte 6.36 1.62 113.0 1. 61 Added ml. benzene.

Solution clear. N 0 Hz evolved upon AI(BH4)3 addition. 7.86 2. 01 2 113. 0 1. 61 Product clear liquid 3 8. 5 after benzene removed. No Hz evolved. 8. 92 2. 28 80. 0 1.61 N 0 Hz evolved.

l Tetra(rnethylamino) diboron.

2 Pressure above the benzene solution. 3 Pressure above product alter benzene removed.

B. In an analogous manner as part A above, when tetra-(di-n-hexylamino)diboron is employed in lieu of tetra(methylamino)diboron, there is obtained an aluminum borohydride adduct of tetra(di-n-hexylamino)diboron.

C. In an analogous manner as part A above, when tris- (cyclohexylamino)borane and beryllium borohydride are employed in lieu of aluminum borohydride and tetra- (methylamino)diboron, respectively, there is obtained a beryllium borohydride adduct of tris(cyclohexylamino)- borane.

Examples 3-6 In the following examples, the theoretical performance of various novel liquid adducts oxidized with nitrogen tetroxide is calculated. The specific impulse values (poundsecond/pound) of these novel propellant systems is compared with hydrazine (also oxidized with nitrogen tetroxide). The data are set forth in Table III infra.

to 14.7 p.s.i., shifting equilibrium, I51) (lb./sec.-lb.).

3 Standard liquid fuel for comparison.

What is claimed is:

1. An adduct of a metal borohydride of the group consisting of aluminum borohydride, beryllium borohydride, and zirconium borohydride, with a ligand of the group consisting of tetra(hydrocarbylamino)diboron, tetra(dihydrocarbylamino) diboron, tris (hydrocarbylamino diborane, and tris(dihydrocarbylamino)borane, said adduct possessing at least one coordinate bond between an amino nitrogen atom and the metal moiety of said metal borohydride.

2. The adduct of claim 1 wherein said metal borohydride is aluminum borohydride.

3. An adduct having the following formula L'[ 4x)-]n wherein L is a ligand of the group consisting of tetra- (hydrocarbylamino)diboron, tetra(dihydrocarbylam-ino)- diboron, tris(hydrocarbylamino)borane, and tris(dihydrocarbyla1nino)borane, wherein M is of the group consisting of aluminum, beryllium, and zirconium, wherein x is the valence of M, wherein n is an integer having a minimum value of one and a maximum value equal to the number of amino nitrogen atoms contained in said ligand, and wherein said adduct contains at least one amino nitrogen atom coordinately bonded to said M.

4. The adduct of claim 3 wherein M is aluminum borohydride.

5. An adduct of aluminum borohydride with tetra- [(lower alkyl)amino]diboron wherein said adduct contains at least one aluminum to amino nitrogen coordinate bond.

6. An adduct of aluminum borohydride with tetra- [di(1ower alkyl)amino]diboron wherein said adduct contains at least one aluminum to amino nitrogen coordinate bond.

7. An adduct of aluminum borohydride with tris-[di- (lower alkyl)amino1borane wherein said adduct contains at least one aluminum to amino nitrogen coordinate bond.

8. An adduct of aluminum borohydride with tris- [(lower alkyl)amino]borane wherein said adduct contains at leats one aluminum to amino nitrogen coordinate bond.

9. An adduct of aluminum borohydride with tetra- (methylamino)diboron wherein said adduct contains at least one aluminum to amino nitrogen coordinate bond.

10. An adduct of aluminum borohydride with tetra- (dimethylamino)diboron wherein said adduct contains at least one aluminum to amino nitrogen coordinate bond.

11. A process which comprises contacting a metal borohydride of the group consisting of aluminum borohydride, beryllium borohydride, and zirconium borohydride; with a ligand of the group consisting of tetra(hydrocarbylamino diboron, tetra dihydro carbylamino diboron, tris(hydrocarbylamino)borane, and tris(dihydrocarbylamino)borane; under an inert, anhydrous atmosphere, and recovering a metal borohydride adduct of said ligand, as the resulting product, from the reaction medium said adduct possessing at least one coordinate bond between an amino nitrogen atom and the metal moiety of said metal borohydride.

12. The process of claim 11 wherein the reaction is elfected at a temperature in the range of from about 64 C. to about +43 C.

13. The process of claim 12 wherein said metal borohydride is aluminum borohydride.

14. The process of claim 13 wherein the maximum concentration of said aluminum borohydride is in slight excess of the quantity that is necessary to react with said ligand, and wherein the resulting product is a liquid adduct of aluminum borohydride and ligand.

15. The process of claim 14 wherein said aluminum borohydride is added, in increments, to said ligand.

16. The process of claim 13 wherein the maximum concentration of said ligand is in slight excess of the quantity that is necessary to react with said aluminum borohydride, and wherein the resulting product is a solid adduct of aluminum borohydride and said ligand.

17. The process of claim 16 wherein said aluminum borohydride is added, in increments, to said ligand.

18. The process of claim 13 wherein essentially stoichiometric amounts of aluminum borohydride and ligand are employed.

19. The adduct of claim 1 wherein said ligand is tetra- (lower alkyl) amino] diboron.

20. The adduct of claim 1 wherein said ligand is tris- (lower alkyl) amino1borane.

(References on following page) 14 References Cited 2,907,781 10/ 1959 Hermelin 260448 UNITED STATES PATENTS 3,014,055 12/1961 Johnson 260448 4/1926 Franklin 1 TOBIAS E. LEVOW, Primary Examiner. 10/ 1933 Spaeth 149-4 5 LEON D. ROSDOL, CARL QUARFORTH, Examiners. 10/1956 Gluesenkamp et a1. 6035.4

J. W. WHISLER, L. A. SEBASTIAN,

Assislamf Examiners.

3/ 1958 Scott et al. 6035.4 

1. AN ADDUCT OF A METAL BOROHYDRIDE OF THE GROUP CONSISTING OF ALUMINUM BOROHYDRIDE, BERYLLIUM BOROHYDRIDE, AND ZIRCONIUM BOROHYDRIDE, WITH A LIGAND OF THE GROUP CONSISTING OF TETRA(HYDROCARBYLAMINO)DIBORON, TETRA(DIHYDROCARBYLAMINO)DIBORON, TRIS(HYDROCARBYLAMINO)DIBORANE, AND TRIS(DIHYDROCARBYLAMINO)BORANE, SAID ADDUCT POSSESSING AT LEAST ONE COORDNATE BOND BETWEEN AN AMINO NITROGEN ATOM AND THE METAL MOIETY OF SAID METAL BOROHYDRIDE.
 11. A PROCESS WHICH COMPRISES CONTACTING A METAL BOROHYDRIDE OF THE GROUP CONSISTING OF ALUMINUM BOROHYDRIDE, BERYLLIUM BOROHYDRIDE, AND ZIRCONIUM BOROHYDRIDE; WITH A LIGAND OF THE GROUP CONSISTING OF TETRA(HYDROCARBYLAMINO)DIBORON, TETRA(DIHYDROCARBYLAMINO)DIBORON, TRIS(HYDROCARBYLAMINO)BORANE, AND TRIS(DIHYDROCARBYLAMINO)BORANE; UNDER AN INERT, ANHYDROUS ATMOSPHERE, AND RECOVERING A METAL BOROHYDRIDE ADDUCT OF SAID LIGAND, AS THE RESULTING PRODUCT, FROM THE REACTION MEDIUM SAID ADDUCT POSSESSING AT LEAST ONE COORDINATE BOND BETWEEN AN AMINO NITROGEN ATOM AND THE METAL MOIETY OF SAID METAL BOROHYDRIDE. 